Implementation work for client_config

- uri parsing
- dns resolution
diff --git a/BUILD b/BUILD
index 438e06b..6e1bec9 100644
--- a/BUILD
+++ b/BUILD
@@ -159,11 +159,15 @@
     "src/core/channel/http_server_filter.h",
     "src/core/channel/noop_filter.h",
     "src/core/client_config/client_config.h",
+    "src/core/client_config/lb_policies/pick_first.h",
     "src/core/client_config/lb_policy.h",
     "src/core/client_config/resolver.h",
     "src/core/client_config/resolver_factory.h",
+    "src/core/client_config/resolver_registry.h",
+    "src/core/client_config/resolvers/dns_resolver.h",
     "src/core/client_config/subchannel.h",
     "src/core/client_config/subchannel_factory.h",
+    "src/core/client_config/uri_parser.h",
     "src/core/compression/message_compress.h",
     "src/core/debug/trace.h",
     "src/core/iomgr/alarm.h",
@@ -270,11 +274,15 @@
     "src/core/channel/http_server_filter.c",
     "src/core/channel/noop_filter.c",
     "src/core/client_config/client_config.c",
+    "src/core/client_config/lb_policies/pick_first.c",
     "src/core/client_config/lb_policy.c",
     "src/core/client_config/resolver.c",
     "src/core/client_config/resolver_factory.c",
+    "src/core/client_config/resolver_registry.c",
+    "src/core/client_config/resolvers/dns_resolver.c",
     "src/core/client_config/subchannel.c",
     "src/core/client_config/subchannel_factory.c",
+    "src/core/client_config/uri_parser.c",
     "src/core/compression/algorithm.c",
     "src/core/compression/message_compress.c",
     "src/core/debug/trace.c",
@@ -397,11 +405,15 @@
     "src/core/channel/http_server_filter.h",
     "src/core/channel/noop_filter.h",
     "src/core/client_config/client_config.h",
+    "src/core/client_config/lb_policies/pick_first.h",
     "src/core/client_config/lb_policy.h",
     "src/core/client_config/resolver.h",
     "src/core/client_config/resolver_factory.h",
+    "src/core/client_config/resolver_registry.h",
+    "src/core/client_config/resolvers/dns_resolver.h",
     "src/core/client_config/subchannel.h",
     "src/core/client_config/subchannel_factory.h",
+    "src/core/client_config/uri_parser.h",
     "src/core/compression/message_compress.h",
     "src/core/debug/trace.h",
     "src/core/iomgr/alarm.h",
@@ -486,11 +498,15 @@
     "src/core/channel/http_server_filter.c",
     "src/core/channel/noop_filter.c",
     "src/core/client_config/client_config.c",
+    "src/core/client_config/lb_policies/pick_first.c",
     "src/core/client_config/lb_policy.c",
     "src/core/client_config/resolver.c",
     "src/core/client_config/resolver_factory.c",
+    "src/core/client_config/resolver_registry.c",
+    "src/core/client_config/resolvers/dns_resolver.c",
     "src/core/client_config/subchannel.c",
     "src/core/client_config/subchannel_factory.c",
+    "src/core/client_config/uri_parser.c",
     "src/core/compression/algorithm.c",
     "src/core/compression/message_compress.c",
     "src/core/debug/trace.c",